Surprising Drought Tolerance of Fir (Abies) Species between Past Climatic Adaptation and Future Projections Reveals New Chances for Adaptive Forest Management

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Surprising Drought Tolerance of Fir (Abies) Species between Past Climatic Adaptation and Future Projections Reveals New Chances for Adaptive Forest Management

Csaba Mátyás^1,*, František Beran², Jaroslav Dostál², JiˇríCápˇ ², Martin Fulín², Monika Vejpustková³ , Gregor Božiˇc⁴ , Pál Balázs¹ and Josef Frýdl^2,*

Citation: Mátyás, C.; Beran, F.;

Dostál, J.; ˇCáp, J.; Fulín, M.;

Vejpustková, M.; Božiˇc, G.; Balázs, P.;

Frýdl, J. Surprising Drought Tolerance of Fir (Abies) Species between Past Climatic Adaptation and Future Projections Reveals New Chances for Adaptive Forest Management.Forests2021,12, 821.

https://doi.org/10.3390/f12070821

Academic Editor: Maciej Pach

Received: 11 May 2021 Accepted: 14 June 2021 Published: 22 June 2021

Publisher’s Note:MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations.

Licensee MDPI, Basel, Switzerland.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://

creativecommons.org/licenses/by/

4.0/).

1 Institute of Environmental and Earth Sciences, Faculty of Forestry, University of Sopron, 9400 Sopron, Hungary; balazs.pal@uni-sopron.hu

2 Department of Biology and Forest Tree Breeding, Forestry and Game Management Research Institute, 252 02 Jílovištˇe, Czech Republic; beran@vulhm.cz (F.B.); dostal@vulhm.cz (J.D.); cap@vulhm.cz (J. ˇC.);

fulin@vulhm.cz (M.F.)

3 Department of Forest Ecology, Forestry and Game Management Research Institute, 252 02 Jílovištˇe, Czech Republic; vejpustkova@vulhm.cz

4 Department of Forest Physiology and Genetics, Slovenian Forestry Institute, 1000 Ljubljana, Slovenia;

gregor.bozic@gozdis.si

* Correspondence: matyas.csaba@uni-sopron.hu (C.M.); frydl@vulhm.cz (J.F.)

Abstract: Research Highlights: Data of advanced-age provenance tests were reanalyzed applying a new approach, to directly estimate the growth of populations at their original sites under individually generated future climates. The results revealed the high resilience potential of fir species.

Background and Objectives: The growth and survival of silver fir under future climatic scenarios are insufficiently investigated at the xeric limits. The selective signature of past climate determining the current and projected growth was investigated to analyze the prospects of adaptive silviculture and assisted transfer of silver fir populations, and the introduction of non-autochthonous species.

Materials and Methods: Hargreaves’ climatic moisture deficit was selected to model height responses of adult populations. Climatic transfer distance was used to assess the relative drought stress of populations at the test site, relating these to the past conditions to which the populations had adapted.

ClimateEUandClimateWNApathway RCP8.5 data served to determine individually past, current, and future moisture deficit conditions. Besides silver fir, other fir species from South Europe and the American Northwest were also tested.Results: Drought tolerance profiles explained the responses of transferred provenances and predicted their future performance and survival. Silver fir displayed significant within-species differentiation regarding drought stress response. Applying the assumed drought tolerance limit of 100 mm relative moisture deficit, most of the tested silver fir populations seem to survive their projected climate at their origin until the end of the century. Survival is likely also for transferred Balkan fir species and for grand fir populations, but not for the Mediterranean species. Conclusions: The projections are less dramatic than provided by usual inventory assessments, considering also the resilience of populations. The method fills the existing gap between experimentally determined adaptive response and the predictions needed for management decisions.

It also underscores the unique potential of provenance tests.

Keywords:climate change; common garden; provenance test; silver fir; grand fir; Balkan firs; drought stress; resilience; climate transfer distance; adaptation

1. Introduction

The rapid change of climatic conditions, which is unprecedented on the scale of the Holocene, across all forest zones, is the greatest challenge to the long-term stability of forest ecosystems and contemporary forest management [1]. The large-scale shift in forest site conditions challenges the ecosystems along with the rear/xeric limits especially [2,3].

Forests2021,12, 821. https://doi.org/10.3390/f12070821 https://www.mdpi.com/journal/forests

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Climatic analyses list subcontinental East-Central Europe among future global climatic hotspots [4]. Compared to the 1981–2010 reference period, climate projections indicate that air temperature e.g., in the Czech Republic will continue to rise by an average of about 1^◦C over the next 30 years. Differences between the emission scenarios will increase after 2050. Compared to the reference period, the annual mean temperature will increase by 2.0^◦C (RCP4.5, —RCP: Representative Concentration Pathway is the greenhouse gas concentration trajectory assumed for various climate change scenarios), respectively, and by more than 4.0^◦C (RCP8.5) until the end of the century. In extensive lowlands, such as in Hungary, more than half of the years may be extremely dry in the last quarter of the present century [5,6]. Less precipitation and higher temperatures in summer threaten the stability of forest ecosystems (Figure1). Droughts lead to growth decline and mortality, particularly among conifers such as silver fir [7,8], and affect the genetic diversity of forest tree populations [9,10].

Figure 1.Expected change of temperature (dT) and precipitation (dP) in the summer quarter (June–

July–August) in southwest Hungary at the xeric limits of silver fir based on the RCP4.5 and RCP8.5 scenarios. Reference: mean of 1971 to 2000. Dots: ensemble means (10 simulations) of the projected changes. Error bars: 66% range of the simulations (original design by B. Gálos, method of calculation described in [6]).

The presence of silver fir has significantly declined in Central Europe in the past century, but only partly for climatic reasons, as acid rain and game damage contributed to the damages.

After the reduction of air pollution across whole East-Central Europe, silver fir recovered significantly despite recent severe droughts. Regarding the future resilience of silver fir, the assessments of its expected response are incongruent. According to some opinions, the species may benefit from winter warming but may suffer from increasing summer droughts, particularly in poor sites at lower elevations [11,12]. Conversely, more optimistic forecasts emphasize the relatively high resilience of silver fir and predict its survival even under increasing stress [13,14]. Furthermore, numerous studies suggest silver fir as a potential alternative species in ecosystems menaced by increasing droughts [7,15–18]. Introducing preadapted populations and even non-native fir species that possess higher drought tolerance has also garnered increasing attention [19,20]. Assisted migration is an ultimate and still debated option [21], gradually finding approval in East-Central Europe. The unknown long- term adaptive capacity of populations transcending their original climatic niche limits is a reason for concern and challenges the sustainability of forests [3,22].

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Provenance trials offer a unique opportunity to explore the inherited potential and limitations of adaptability, allowing for conclusions about drought stress responses of populations exposed to climatic changes mimicked by geographical transfer [23,24]. Test sites close to the xeric (rear) edges of species distribution are particularly promising locations to analyze phenotypic responses to drought stress.

Although questioned by some authors [25,26], the between-population adaptive diversity of silver fir has been proven in provenance tests, but the long-term potential of the species coping with the projected climatic scenarios has not been sufficiently explored.

Many of the existing studies were written before gridded climate data became available (e.g., [27–30]). Some results originate from greenhouse/nursery trials [25,31–33] or tests at juvenile age [34]. Since the advent of advanced analysis methods, a plethora of genomic, evolutionary, ecological, phenological, and physiological data improve the awareness of factors determining the adaptation of populations. Concurrent to the adaptive origin of differentiation, interfering historic/evolutionary effects are frequently discussed [35–37].

The assessment of phenological responses in the setting of projected climatic conditions, a precondition for management decisions is, however, still missing.

In this study we concentrate on a single phenotypical trait, height measured at an advanced age, to evaluate long-term adaptive responses of fir species and provenances.

We apply a robust climate index to infer drought tolerance profiles for current and future conditions. The aim was to fill the existing gap between experimentally determined adaptive potential and predictions needed for management decisions [6]. The study is based on the reanalysis of results of three older provenance trials of fir species in the Czech Republic [20]. The specific value of the data, measured at an advanced age, justified a closer investigation of the phenotypic response of populations to climatic warming and droughts. The populations in the three trials include provenances of differentAbiesspecies of regional interest for adaptation/mitigation decisions in forestry practice. Native silver fir was the focus, represented by provenances from the drought-threatened part of the distribution in sub-continental East-Central Europe. The trials also contain other fir species from Southern Europe and from the American Northwest, which could be of potential use for future introductions.

First, we focused on detecting responses to the climatic conditions the populations were exposed to in the trials rather than on the ranking of populations. Height at an advanced age was interpreted as the joint result of the selection driven by past climatic factors at origin and by the response to “current” climate from planting until the last measurement. Geographic provenance data were used exclusively in the context of climatic factors; thus, transfer distances were expressed only in climatic terms. Second, a climate indicator available from harmonized, gridded datasets for selected time periods was chosen to model the observed and predicted responses. Climate projections were derived uniformly for the trial sites and the locations of origin. Third, drought tolerance profiles established in the trials were utilized to estimate the potential of fir species and provenances in the setting of a selected climate scenario for the subcontinental zone in East-Central Europe.

2. Materials and Methods

2.1. Description of the Three Provenance Trials

The Forestry and Game Management Research Institute (FGMRI) established three provenance trials of fir species in the Czech Republic between 1976 and 1984. The trials contain a selection of provenances of Euro-Mediterranean and North American species [38,39].

The Písek trial, organized by the FGMRI, contains native silver fir (A. albaMill.) and other fir species from the Balkan and the Mediterranean (Table 3). As part of a series initiated by IUFRO, an extensive collection of 24 coastal and inland provenances of grand fir (A. grandis(Dougl. Ex D. Don) Lindl.) was established in Zbiroh (Table 4). The trial Dražiˇcky, belonging to another international IUFRO series, contains provenances of grand fir and noble fir (A. proceraRehder) (Table 5). (Latin names are used in the text only for the less known Balkan and Mediterranean

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fir species.) Geographic data and maps of the populations’ provenance, historic and site details of the trials, as well as all data measured in 2015 are found in Frýdl et al. [20].

Similar to most other provenance tests, the trials are far from being fully representative for any of the species and make only limited comparisons possible. The specific value of these trials is that they were maintained and measured until nearly mature age (32 to 40 years), and, even more importantly, the trials are typically located in climatic environ- ments close to the warm and dry xeric limits of silver fir. (The term xeric limit is preferred as an alternative for rear or trailing limit, to describe the low-elevation, drought-threatened limit of distribution to emphasize the primary role of water scarcity at these borders.) The chosen low-elevation sites were nearly offsite conditions for someAbiesspecies and provenances. Such data are very rare and facilitate the “space-for-time” assessment of growth and resilience, even in the absence of mortality observations.

2.2. Source of Data and Method of Analysis

The data of measurements from 2015, which are the basis of the present analysis, have been evaluated by the FGMRI and published by Frýdl et al. [20]. The three trials were investigated individually due to different sets of species and populations. From among the different quantitative traits observed, height consequently yielded the lowest error variation and the best differentiation among populations. In genetic field tests, the high heritability of height has proven its relative independence from environmental and human-caused effects. Therefore, mean height was selected to investigate the sensitivity of provenances to drought.

Phenotypic responses were interpreted as effects of climatic change mimicked by geographic transfer and analyzed by applying the ecodistance concept [24]. “Ecodistance”

(here: climatic transfer distance) is defined as the difference between the ecologically relevant variables (in this case, climate) at the test site and the population provenance (origin); i.e., the difference between the conditions undergone by the populations in the experiment and the conditions they had adapted to in the past. Positive differences indicate a transfer to drier and/or warmer sites (=mimicked climatic warming); negative values signify transfer to cooler and/or wetter sites (=mimicked climatic cooling). The 0 value stands for a climate equivalent to that at the site of provenance [40].

Climatic transfer distance is interpreted as the indicator ofrelative drought, individually undergone by populations at the test site, compared to the drought stress they were adapted to in the past. In this sense, the value of relative drought is different for every provenance.

To determine climatic transfer distances, the mean of the period from outplanting until the time of measurement was calculated for the “current climate” conditions at the test site. The length of the averaged period was different for each test because the planting years varied, while measurements were made in the same year, in 2015 (Table1). The reference period for the “past climate at provenance” was set uniformly for 1911–1940. The selected 30-year period covers roughly the middle third of the approximate age (80–100 years) of selected populations from which seeds were harvested. At that age, within-population competition has largely formed the genetic structure of the stand. Climate analyses also indicate that this is the last time period of the Holocene before the onset of global anthropogenic effects [41,42]. Thus, it was taken as the basis for representing past secular adaptation.

Table 1.Basic data of the three trials and their mean height and tree density in 2015. Adapted from [20].

Trial Name Year of Planting

Altitude (m)

Longitude (Decimal)

Latitude (Decimal)

Age at Mea- surement

(years)

Trial Mean Height

(m)

Mean Tree Density (% from Planted)

Písek 1976 395 14.33^◦E 49.27^◦N 40 15.49 28.5^a

Zbiroh 1980 450–460 13.64^◦E 49.79^◦N 36 19.26 50.1

Dražiˇcky 1984 485 14.59^◦E 49.39^◦N 32 14.54 55.9

awithout three Mediterranean populations, showing 100% mortality.

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Accordingly, climatic transfer distance, i.e., relative drought, was determined for climatic moisture deficit (dCMD) as

dCMD= [current value at test site]−[past value at provenance]

The “current climate” of the Czech test sites was determined using the data of nearby (Czech) meteorological stations. The distances to the nearest meteorological stations were small, and corrections were unnecessary (TableA1). In this study, year-to-year growth (increment) variations or annual weather fluctuations were not the objects of analyses as the focus was on height response attained at the final measurement, determined by long- term means. Besides the annual precipitation and temperature fluctuations, the weather conditions in the course of the trial maintenance have also shown a significant trend of rising temperatures and recurrent drought years. Summer temperature means at the trial sites of Písek and Dražiˇcky increased by 1.3^◦C, from 16.6 to 17.9^◦C. At the Zbiroh site, the increase reached 1.9^◦C. Extremely hot summers were observed at all three trial sites in the years 1992, 1994, 2003, and 2015. Consequently, the climatic moisture deficit has increased during the “current” climate period in all three trials. Nevertheless, the extreme weather conditions did not lead to conspicuous mortality differentiation, with the exception of the Mediterranean fir species in the Písek trial.

Data for past climates were obtained from two databases. For the Euro-Mediterranean locations, the recently published databaseClimateEU(version 4.80) [43] was utilized. It contains historic climate data for Europe using 15 global climate models, for a representative set of climate variables, for the last 120 years (1901 to 2019) as well as multi-model CMIP5 climate change projections for the 21st century. The similarly developed software package ClimateWNA(version July 2020) [44], which also contains historical data and future projections, served to downscale past climate variables for western North American populations of firs in the trials. Scale-free, actualized climate datasets from both databases were downscaled courtesy of T. Wang (UBC Vancouver). During the course of the digital interpolation of past climate data, it became apparent that in numerous cases the original coordinates of sampled forest stands were incorrect. Consequently, the nearest point at proper altitude served to estimate the climate parameters; the actual land cover shown on Google was taken also into consideration. Climate data and executed corrections are indicated in Tables 3–5. Due to the different methods of determining climate parameters, the climate data in this study are not identical to those in Frýdl et al. [20].

Hargreaves’ climatic moisture deficit (CMD) was selected to calculate the climatic transfer distances. This bioclimatic variable was calibrated originally for estimating potential evaporation relative to precipitation under semi-arid agrarian conditions [45]. Compar- isons of results with other, straightforward variables have indicated thatCMDis also well suited for describing drought stress under forest conditions. The comparison of response regressions usingCMDvalues both for annual and summer periods surprisingly indicated that annualCMDvalues yielded higher determination coefficients, so these were selected for the calculation of climatic transfer distances (dCMDann). Hargreaves’CMDmeans of 30-year periods were available from both databases (ClimateEUandClimateWNA). The climatic transfer distances expressed as differences ofCMDvalues (dCMD) were calculated not only for current vs past climates but also for future climatic changes. The transfer distances of the two basic variables, temperature, and precipitation, are shown in AppendixA to illustrate their contribution to the responses at the test sites (FiguresA1–A3).

The statistical analysis of the trials was performed using theQC.Expert3.1 [46] and NCSS10 (version: 10.0.6) programs [20]. Due to the non-normality of the data, the differences among provenances were tested using the Kruskal-Wallis one-wayANOVAtest.

Regressions were calculated between height and climatic transfer distance of provenances//

but were presented only if statistically significant and biologically appropriate. Thesetoler- ance profilesare transfer functions (even if shown only as scatter of data points), comparing the responses of different populations in the same common garden test. They have to be distinguished from reaction norms ofindividualpopulations expressing their phenotypic

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plasticity across numerous test sites [40]. Lacking data of similar-age parallel trials, the results did not allow for the calculation and comparison of reaction norms. However, the tolerance profile of species, i.e., the variation of phenotypic response between differ- ently adapted provenances, offers a hint to estimate the species-specific range of climatic resilience and allows certain comparisons between species.

3. Results

Tables1and2show the main data of the test sites and their mean height and mean density (remaining percentage from planted) measured in 2015. Tree density numbers were the lowest at the driest site Písek, partly due to the higher age of the trial. The density data could not be used for inferring survival differentiation between provenances. The reasons were the absence of extreme events triggering significant mortality and the routine silvicultural tendings, applied to keep relatively even competition conditions in the trials.

Partly due to the relatively small plot size for the advanced-age trees, the rather strong differentiation of tree numbers per plot could not be linked to climate factors, with a few exceptions (discussed later).

Table 2.Current climate parameters of the three provenance tests, calculated according to the described protocol.

Trial Name

Annual Mean Temp.

(^◦C)

Mean Temp. in Warmest Quarter

(^◦C)

Annual Mean Precip.

(mm)

Mean Precip. in Warmest

Quarter (mm)

Mean Annual Moisture Deficit

(CMD_ann)

Písek 8.1 17.2 570 229 213

Zbiroh 8.1 17.0 595 241 179

Dražiˇcky 8.1 17.3 592 229 189

The results of the Kruskal-Wallis one-wayANOVAtests rejected the hypothesis of equal mean heights at thep≤0.05 level for all three experiments. Matrices of significance, based on the obtained statistics are presented in AppendixAin FiguresA4–A6. The statistics have proven significant differences mostly at the level of provenance groups. The significance of differences might be underestimated due to the applied one-wayANOVAtest.

Contemplating climatic transfer distances (dCMDann), i.e., relative drought values at the trial sites, annual climatic moisture supply was sufficient or even advantageous for some populations, first due to the summer rainfall maxima typical for Central Europe.

Table2summarizes the main climatic data of the three Czech test sites for the “current climate” period. Data of provenances are presented in Tables3–5.

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Table 3.Basic data of the provenance trial 64, Písek: species and populations represented and basic data used for analysis (sequence and geographic data of provenances are identical to the source publication (Adapted partly from [20]). Climate distances refer to the trial location.

Populations of the Provenance Trial 64 Písek, CZ Past Climate at Origin (1911–1940) Climate Distance (D) Data 2015

Prov No. AbiesSpecies

Name Provenance Name Alt. (m) Long. E Lat. N

January Mean Temp.

(^◦C)

Annual Mean Temp.

(^◦C)

Mean Temp.

Warmest Quarter (^◦C)

Annual Mean Prec.

(mm)

Mean Prec.

Warmest Quarter (mm)

CMD(mm, Ann.)

Temp.

Change Warmest Quarter (^◦C)

Prec.

Change Warmest Quarter (mm)

dCMD (Index Change,

mm)

Mean Height

(m)

Mean Tree Density (% From Planted)

74 A. alba Milevsko, Kluˇcenice CZ 410 14.2^◦ 49.6^◦ −2 8.4 17.3 492 189 284 −0.1 40.0 −71 17.19 22.0

81 A. alba VyššíBrod, Vítk ˚uv Kámen CZ 900 14.3^◦ 48.6^◦ −4.2 5.9 14.5 854 296 122 2.7 −67.0 91 15.47 10.0

89 * A. cilicica Kammouha LIB 1100 36.0^◦ 34.0^◦ 6.3 14.9 22.2 1167 4 763 −5.0 225.0 −550 0.00 0.0

109 A. cephalonica Centr. Peloponnese, Vytina GR 1250 22.1^◦ 37.6^◦ 1.9 10.9 18.7 794 51 573 −1.5 178.0 −360 14.19 29.3

121 * A. cilicica Djebel el Chouk, Lattakia SYR 1300 36.0^◦ 35.8^◦ 2.2 12.6 20 1039 24 525 −2.8 205.0 −312 0.00 0.0

130 A. alba Nasavrky, Podh ˚ura CZ 370 15.8^◦ 49.8^◦ −2.7 8.2 16.8 487 196 253 0.4 33.0 −40 16.89 32.7

132 * A. alba Rilskije gory, Borovec BG 1200 23.6^◦ 42.2^◦ −3 7.3 15.7 515 137 362 1.5 92.0 −149 16.85 31.3

135 * A. pinsapo Malaga, La Yunquera ES 878 4.7^◦W 36.7^◦ 6.8 14.7 22.2 633 18 711 −5.0 211.0 −498 0.00 0.0

136 A. cephalonica Peloponnese, Vytina GR 1010 22.2^◦ 37.7^◦ 3.4 12.2 20 753 48 626 −2.8 181.0 −413 14.34 34.7

137 * A. borisii-regis Mt. Pindos, Pertuli GR 1200 21.3^◦ 39.8^◦ −0.3 9.6 18.2 727 88 503 −1.0 141.0 −290 14.59 35.3

223 * A. alba Sanski Most BH 1050 16.6^◦ 44.6^◦ −3.5 6.9 15.3 943 226 170 1.9 3.0 43 15.61 28.0

228 * A. alba Regello, Vallombrosa IT 1010 11.5^◦ 43.7^◦ 0.2 9.5 17.5 967 163 180 −0.3 66.0 33 14.82 30.7

S 2 * A. alba BanskáBystrica, Radva ˇn SK 780 19.0^◦ 48.7^◦ −5.1 6.4 15.1 759 258 152 2.1 −29.0 61 14.92 31.3

Data and current climate of the test site ** 395 14.3^◦ 49.2^◦ −1.5 8.1 17.2 570 229 213 15.49 28.5

Climate data for Kammouha, LB were estimated from Worldclim database, 1961–1990; * Corrected locations ** CZ met data (original or corrected). Last row: numbers in italics indicate averages excluding the populations with 0.0 values.

Table 4.Basic data of the provenance trial 213 Zbiroh: location and climate of grand fir populations used for analysis (sequence and geographic data of provenances are identical to the source publication (Adapted partly from [20]). Climate distances refer to the trial location.

Populations of the Provenance Trial 213 Zbiroh, CZ Past Climate at Origin (1911–1940) Climate Distance (D) Data 2015

Name Provenance Name Alt. (m) Long. W Lat. N

(^◦C)

Mean Temp.

(mm)

Mean Prec.

CMD(mm, ann.)

Temp.

Prec.

mm)

Mean Height

(m)

12040 A. grandis Salmon River CAN/BC * 50 125.8^◦ 50.3^◦ 0.6 8.4 15.6 1444 150 211 1.4 91.0 −32 21.81 44.0

12041 A. grandis Oyster Bay CAN/BC 5 125.2^◦ 49.9^◦ 1.2 9.1 16.3 1137 121 286 0.7 120.0 −107 20.90 70.0

12042 A. grandis Buckley Bay CAN/BC 45 124.9^◦ 49.5^◦ 0 8.8 16.3 1391 87 319 0.7 154.0 −140 19.32 62.0

12043 A. grandis Sproat Lake CAN/BC 25 125.0^◦ 49.3^◦ 0.8 9.4 17 1827 117 293 0.0 124.0 −114 20.05 58.0

12044 A. grandis Kay Road CAN/BC 50 124.3^◦ 49.3^◦ 2 9.4 16.5 863 85 342 0.5 156.0 −163 20.02 72.0

12045 A. grandis Yellow Point CAN/BC 30 123.8^◦ 49.1^◦ 2.7 9.7 16.6 916 81 335 0.4 160.0 −156 20.03 57.0

12046 A. grandis Mount Provost CAN/BC 75 123.8^◦ 48.8^◦ 1.8 9.5 16.7 1199 78 353 0.3 163.0 −174 21.38 63.0

12047 A. grandis Sooke CAN/BC 20 123.8^◦ 48.4^◦ 2.9 9.6 14.9 1111 72 296 2.1 169.0 −117 20.05 60.0

12002 A. grandis Tulalip USA/WA 30 122.3^◦ 48.1^◦ 3.4 9.5 14.8 651 53 369 2.2 188.0 −190 22.29 48.0

12003 A. grandis Indian Creek USA/WA 140 123.6^◦ 48.1^◦ 2.1 9 14.7 1011 64 334 2.3 177.0 −155 21.48 57.0

12004 A. grandis Gardiner USA/WA 30 122.9^◦ 48.1^◦ 2.9 9.6 15.2 497 61 401 1.8 180.0 −222 21.72 56.0

12006 A. grandis Eagle Creek—low USA/WA * 760 120.6^◦ 47.7^◦ −4.2 7.6 17.8 831 56 531 -0.8 185.0 −352 19.05 46.0

12008 A. grandis Jack Creek USA/WA * 825 120.8^◦ 47.3^◦ −3.7 6.6 15.9 877 56 487 1.1 185.0 −308 17.30 43.0

12011 A. grandis Clear Lake USA/WA * 945 121.3^◦ 46.6^◦ −3.8 5.4 14 948 69 394 3.0 172.0 −215 17.89 48.0

12013 A. grandis Cooper Spur USA/OR 1040 121.7^◦ 45.5^◦ −1.9 6.7 14.8 2097 115 232 2.2 126.0 -53 18.91 36.0

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Table 4.Cont.

Populations of the Provenance Trial 213 Zbiroh, CZ Past Climate at Origin (1911–1940) Climate Distance (D) Data 2015

Name Provenance Name Alt. (m) Long. W Lat. N

(^◦C)

Mean Temp.

(mm)

Mean Prec.

CMD(mm, ann.)

Temp.

Prec.

mm)

Mean Height

(m)

12015 A. grandis Sisi Butte USA/OR * 975 121.8^◦ 44.9^◦ −0.8 7.4 15.2 1595 98 318 1.8 143.0 −139 18.19 36.0

12016 A. grandis Santiam Summit USA/OR 1400 121.9^◦ 44.4^◦ −2.2 5.5 13.1 2033 127 266 3.9 114.0 −87 16.22 34.0

12019 A. grandis Roaring River USA/OR * 1310 122.0^◦ 43.5^◦ −0.7 6.8 14.3 1733 129 286 2.7 112.0 −107 17.88 24.0

12020 A. grandis Crescent Creek USA/OR * 1375 121.9^◦ 43.5^◦ −2.7 5.7 13.6 782 56 524 3.4 185.0 −345 17.90 24.0

12025 A. grandis Buckskin Creek USA/ID * 1220 116.2^◦ 48.0^◦ −5.4 4.8 14.4 1087 129 304 2.6 112.0 −125 14.55 56.0

12026 A. grandis Plummer Hill USA/ID 850 116.9^◦ 47.3^◦ −3.2 7.6 17.3 642 80 511 -0.3 161.0 −332 16.96 20.0

12031 A. grandis Bertha Hill USA/ID * 1430 115.8^◦ 46.8^◦ −4.4 5.7 15.5 1341 120 307 1.5 121.0 −128 18.17 63.0

12038 A. grandis Clearwater USA/ID * 760 115.4^◦ 46.6^◦ −3.5 7.9 18.3 965 114 479 −1.3 127.0 −300 21.48 72.0

12037 A. grandis Stanley Creek USA/MT * 800 115.9^◦ 48.3^◦ −5.4 6.1 16.1 698 97 494 0.9 144.0 −315 18.58 53.0

Data and current climate of the test site ** 456 13.64^◦E 49.79^◦ −1.4 8.1 17.0 595 241 179 19.26 50.1

* Corrected locations, ** CZ met data (original or corrected).

Table 5.Basic data of the provenance trial 219 Dražiˇcky: location and climate of species and populations used for analysis (sequence and geographic data of provenances are identical to the source publication (Adapted partly from [20]). Climate distances refer to the trial location.

Populations of the Provenance trial 219 Dražiˇcky, CZ Past Climate at Origin (1911–1940) Climate Distance (D) Data 2015

Prov No. Abies Species

Name

Provenance Origin, Name Alt. (m) Long. W Lat. N

(^◦C)

Annual Mean Temp. (^◦C)

Mean Temp.

Annual Mean

Prec.

(mm)

Mean Prec.

CMD (mm, ann.)

Temp.

Prec.

mm)

Mean Height

(m)

CZ 0 A. alba Adršpach CZ 620 16.1^◦E 50.6^◦ −5.1 6.2 14.6 590 231 137 2.7 −2.0 52.0 6.22 32.0

12001 A. grandis Buck Creek (Skamania) USA/WA 400 121.4^◦ 48.3^◦ −0.6 8.5 16.5 2291 174 199 0.8 55.0 −10.0 20.65 74.0

12002 A. grandis Tulalip (Ellensburg) USA/WA 30 122.3^◦ 48.1^◦ 3.4 10.2 16.1 909 111 296 1.2 118.0 −107.0 19.75 66.0

13004 * A. procera Mary’s Peak USA/OR 1065 123.6^◦ 44.5^◦ 2.8 9.6 16.1 3060 89 269 1.2 140.0 −80.0 12.41 44.0

13006 * A. procera Snow Peak USA/OR 1060 122.6^◦ 44.6^◦ 1.5 7.9 14.3 2532 173 177 3.0 56.0 12.0 13.68 42.0

13011 * A. procera Larch Mtn. USA/OR 975 122.1^◦ 45.5^◦ −0.3 7.2 14.2 2969 209 157 3.1 20.0 32.0 14.42 68.0

13014 * A. procera Red Mtn. USA/WA 1220 121.8^◦ 45.9^◦ −2.4 5.4 13 2489 150 171 4.3 79.0 18.0 14.53 63.0

13018 A. procera McKinley Lake USA/WA 900 122.1^◦ 46.6^◦ −0.4 7 14.2 2175 184 162 3.1 45.0 27.0 15.16 64.0

13021 * A. procera Stevens Pass USA/WA 1000 121.1^◦ 47.7^◦ −3.8 5.1 13.2 2075 159 185 4.1 70.0 4.0 14.00 50.0

Data and current climate of the test site ** 488 14.59^◦E 49.39^◦ −1.8 8.1 17.3 592 229 189 14.54 55.9

* Corrected locations, ** CZ met data (original or corrected).

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3.1. Comparison of Euro-Mediterranean Fir Species and Provenances in Trial 64, Písek

The trial contains seven populations of silver fir and six other fir populations from Southern Europe and the Near East (Table3). The silver fir (Abies albaL.) provenances represent a geographically and climatically differentiated set of locations, mostly from the drought-threatened subcontinental part of the species distribution, which enabled the modelling of the intra-specific effect of growing drought stress across climates. The species were separately analyzed.

Five out of the seven silver fir populations in the Písek test (VyššíBrod/CZ, Sanski Most/BH, BanskáBystrica/SK, Borovec/BG and the Sub-Mediterranean Regello/IT) are higher-altitude provenances (>700 m a.s.l.), with lower annual temperatures and higher precipitation than at Písek, with the exception of the extremely dry location at Borovec/BG.

The two Czech low-elevation sources (<500 m a.s.l., Milevsko and Nasavrky) were transferred to a climate similar to their origin (Table3, Figure2, FigureA1a,b). The Italian provenance is the only population outside the subcontinental climate zone (Figures2and3).

Higher altitude provenances are adapted to less moisture deficit stress, appearing mainly during the summer months. Their transfer to the test site Písek caused increased exposure to relative (provenance-related) drought, causing weaker growth response. The low-elevation populations were more stressed at their origin, where the water supply deficit is also significant in the spring and autumn months. Their relative drought stress at Písek was less; thus, their height growth response was better. The response of the high-elevation Bulgarian population from Borovec, Rila Mts. (1200 m a.s.l.) is specific; at its provenance annual precipitation is only 515 mm, and the annualCMDamounts to 362 mm.

It is adapted to high moisture deficit also outside the summer season. Consequently, its response was similar to low-elevation populations, indicating high drought tolerance (Table3, Figure2). The Sub-Mediterranean population Regello (IT) displayed a weak drought tolerance close to the other high-elevation populations; its annualCMDat origin is just half of the Bulgarian provenance (180 mm, Table3).

Figure 2. Mean height response and unilateral transfer equation of silver fir provenances to climate transfer distance (current vs past) expressed in annual moisture deficit units (mm precipitation,dCMDann) in the trial Písek. The regression is significant atp≤0.05.

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Figure 3.Mean height response of all provenances to climate transfer distance (current vs past) expressed in annual climatic moisture deficit (mm precipitationdCMDann) in the trial Písek. The provenancesA. cilicicaandA. pinsapoare not shown, having suffered total mortality (see also FigureA1a,b for distances expressed in temperature and precipitation changes).

Thus, a connection between height growth, respectively, drought tolerance at an older age, and the climate at origin to which the populations were adapted was detected. The annualCMDvalues have shown a better correlation with height response than the summer values. The calculated regression is exponential and attains a significant R²value (0.705, p≤0.05). The equation is unilateral, i.e., it shows the change of growth response towards only one limit of tolerance, here towards the xeric limit [40]. The regression mean height vs.dCMDannindicates the best height response for provenances with origins close to the test site, but the example of Borovec (BG) shows that transferred populations may attain similar performance. The result implies a considerable climate sensitivity of silver fir, which should be treated with caution as the result is based on only seven populations.

The Kruskal-Wallis test matrix (FigureA4) supports the credibility of the result. The test demonstrated significant differences in height growth of silver fir by elevation and region;

high elevation populations appeared set apart from the low-elevation Czech populations Milevsko and Nasavrky (74, 130), indicating effective local adaptation by altitude.

The comparison of all provenances in the Písek test shows a completely different pic- ture (Figure3). The three provenances from the Balkan species (A. borisii-regis, A. cephalonica, 109, 136, and 137) enjoyed a considerably cooler/wetter summer climate than at their origin. They responded with slower growth and shared this response with two silver fir populations transferred from locations further to the south than Písek; these are the high- elevation Slovak (S2 Radva ˇn) and Italian (228 Regello) populations. The Kruskal-Wallis test confirmed their height growth to be significantly weaker, but there was no significant difference between them (Figures3andA4). The climate tolerance profile of Balkan populations displays high moisture surplus (negativedCMDann) values and does not show any trend linked to changing surplus moisture supply at Písek.

It is remarkable thatA. cilicicaandA. pinsapopopulations from geographically distant and climatically extreme locations did not survive the climate of the test site (Table3). The total mortality of these populations is most likely due to winter and late frosts, which were considerably harsher than at their original sites [38]. The January mean temperature at the origin of these populations is over 0^◦C (2.2–6.8^◦C), while the summer mean precipitation is extremely low; e.g., forA. cilicicafrom Kammouha, Lebanon, it amounts to only 4 mm (Table3). The calculated high “surplus moisture” (dCMDannin Table3) played no role in preventing their mortality.

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For the projection of future performance of silver fir provenances in the digital space of climate models, we used the unilateral transfer equation of silver fir, calculated for the

“current climate” as a basis. Extending the equation for the periods 2041–2070 and 2071–

2100, estimations of height responses are achieved for the second half of the 21st century.

For the sake of comparison, the future height data are shown uniformly for the age in the year 2015, i.e., in the sense of a site index at the age of 40 years, i.e., in 2015. The multi-model ensemble climate data inClimateEUunder the high-emission RCP8.5 and the less stringent mitigation RCP4.5 pathways were used both for the original locations of provenance and for the test site in Písek. The mid-century projections (2041–2070) did not show climatic changes substantial enough to warrant them being analyzed separately. Furthermore, only the results of the pathway RCP8.5 for the period 2071–2100 are displayed (Figure4, TableA3). The pessimistic high-emission pathway was preferred as it was considered more realistic, considering also unknown physical and biological risks expected to affect the resilience of populations in the future.

Figure 4. Current and the future climatic transfer distance and mean height response of silver fir provenances in the Písektrial. Their performance is compared under two transfer situations, current heights at the test site (data measured in 2015, blue dots) and projected heights (climate period 2071–2100, derived fromClimateEU, pathway RCP8.5, red dots). The transfer equation for current vs past climate was extrapolated for future data. The horizontal axis shows climate transfer distances (precipitation mm deficit). For the sake of comparison, current and future heights are both presented as the site index value for the age of 40 years, i.e., in 2015.

The projected response of the silver fir populations to the change of climate in the period 2071–2100 was calculated with the transfer equation gained for the current vs.

past climates, assuming its validity for the whole century (Figure4). The virtual transfer changed the climate distance by approximately +100 mm moisture deficit increase for all populations. Height response shifts of provenances from current to future climates are basically of the same magnitude, but follow the exponential character of the equation;

the height of the provenances that already had moisture deficits in the current climate experienced stronger declines under future conditions. The populations with extreme moisture deficit attained the lowest projected heights, and the responses reveal the most vulnerable populations. These are all high-altitude populations, adapted to milder drought stress of shorter duration: the Czech VyššíBrod (81), the Slovak Radva ˇn (S2), further the

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Italian Regello (228) and the Bosnian Sanski Most (223). The high-altitude provenance Borovec (132) is adapted to a high moisture deficit at its origin and may attain a top position in Písek under the future climate (TableA3). No transfer equation is available for the Balkan fir species due to their currently sufficient moisture supply (Figure 3).

Assuming a drought stress change of similar magnitude, i.e., a transfer shift (dCMDann) of approximately 100 mm, all populations remain in the sufficient moisture supply zone in the period 2071–2100. This predicts a low drought stress exposure in the future for the high-altitude Balkan populations. The future performance of distant Euro-Mediterranean provenances cannot be estimated due to a lack of data in parallel test locations in milder climates.

A further step is to estimate the population performance at their locations of origin, which is also calculated with the help of the equation for “current” vs. past data for silver fir, here using the climate projections for the individual sites of origin, run for the 2071–2100 period, using the databaseClimateEU,pathway RCP8.5. While the climate projection for the future was the same for all populations in the Písek test, here every provenance has a different climate projection according to its original geographic location. (The differences in local site potential between the locations of provenance are not considered.) Comparing Figures4and5, the scatter of projected points appears less drastic for the sites of origin (Figure5), and their rank is different due to the change of the reference location.

Figure 5.Comparison of current height at Písek and estimated future mean height response to climatic change of silver fir populations at their original location of provenance. Their performance is compared under two climatic transfer situations, current heights at the test site (data measured in 2015, blue dots) and projected heights at origin in the climate period 2071–2100 (derived fromClimateEU, pathway RCP8.5, red dots). The transfer equation for current vs past climate was extrapolated for future data. The horizontal axis shows climate distances indCMDunits (mm precipitation deficit). For the sake of comparison, both current and future heights appear as the site index value for the age of 40 years, i.e., in 2015.

The projections reveal the most vulnerable populations at their origins at the end of the century. The change of the position of provenance 81 (VyššíBrod CZ) is notable, as it shows best the differentiation caused by individually projected climates. The high-elevation population has responded with weak height in Písek, and its survival at the test site was the lowest. The projected climatic position at the original high-elevation site is, however, very suitable: −39 mm moisture deficit (i.e., moisture surplus), and the expected response is the best-projected height: 17.13 m (TableA4). The silver fir provenance with the highest

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drought tolerance, the Bulgarian Borovec (132), will suffer from an extreme moisture deficit increase of +172 mm at its origin. Its projected height response is the lowest with 13.0 m.

While it may survive in Písek, it will most likely go extinct in Bulgarian Borovec. Thus, the population will be more threatened by droughts at its original location than in the low-elevation site Písek towards the end of the century. Other populations with extreme moisture deficit are the Italian Regello and the Bosnian Sanski Most; both were among the weak performers also in the Písek trial. The two Czech low-elevation provenances of Nasavrky and Milevsko, as well as the Slovak Radva ˇn, will maintain their medium positions at their original location. In the case of the Balkan fir species, projections were calculated by the same equation for silver fir. Although their predicted relative drought change is above the assumed survival limit of 100mm (for details, see the discussion), their currentdCMDannvalues are so low that they will remain in the high moisture surplus zone at their origin, similar to the Písek trial location (Figure3, TableA4).

3.2. Comparison of Grand Fir Provenances in Trial 213, Zbiroh

The trial contains 24 provenances of grand fir, among them 8 from Vancouver Island, Canada, three from the coastal belt north of Seattle, WA, and 16 sources from the Inland NW of the USA, representing higher altitude stands from the Cascades and the inland range in Idaho and Montana (Table4). The shortcoming of this rather detailed collection of provenances is it contains no control populations of native silver fir in the trial; nonetheless, the within-species mean heights are worth comparing, in view of their possible use in East-Central Europe.

The Canadian sources all originate from low elevations of the eastern coast of Vancou- ver Island and receive high annual rainfall above 1000 mm, but low summer precipitation (94–229 mm). The three populations from coastal Washington (USA) enjoy somewhat less annual precipitation but also lower summer rainfall. The Cascade sources have similar rainfall ranges, while inland provenances in Idaho and Montana receive less annual precipitation (684–933 mm). Temperature conditions across the huge range from mild-coastal to continental-inland climates are relatively comparable in summer with means of 12.6–

17.4^◦C, while January mean temperatures show larger differences between coastal and inland locations (between 3.8 and−6.0^◦C). All climate data related to the past reference period 1911–1940 (Table4).

The Kruskal-Wallis test results for mean heights quite clearly differentiate two main groups within the grand fir provenances. The first main group contains coastal populations from Vancouver Island (reg. numbers 12040 to 12047) and Puget Sound, Washington, USA (12002 to 12004). The latter populations display the best growth from all tested provenances. The second main group originates partly from higher elevations (>700 m) of the Washington and Oregon Cascades (12006 to 12020), with significantly weaker growth, while the populations from inland Idaho and Montana (12026 to 12031) form an overlapping heterogeneous group, representing highly variable ecological conditions and discontinuous ranges in the Rocky Mts. A significant outlier is Clearwater, Idaho (12038), a top grower (FigureA5).

In the trial of Zbiroh, “current” temperature conditions at the trial site (annual mean of 8.1^◦C and summer mean 17.0^◦C) are within the data range of the sources from the American Northwest. The amount and distribution of rainfall is, however, notably different.

“Current” annual precipitation amounts to only 595 mm in Zbiroh, but over one-third of these falls in the summer quarter (241 mm), producing a summer rainfall peak.

It is very illustrative to compare the climate charts of the weather stations at Zbiroh and Everett, a coastal station in the state of Washington, USA. The data for the charts were derived from [47], drawn by theClimateChartapplication (climatecharts.net) accessed on 10 November 2020. Figures6and7display the diametrical difference of the climate of Central-Southeast Europe versus the mild, oceanic “Sub-Mediterranean type” climate along the inland coast of Washington State (Puget Sound). At the test site, most grand fir provenances experienced a drastic decrease in their annual precipitation with the exception

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of inland sources, where the decrease was less (Table4). The mean summer rainfall at Zbiroh, however, was higher. These differences caused all provenances to experience a wetter and warmer summer climate at the test site than at origin (Figure8, FigureA2a,b).

Adapted to relatively dry summers, grand fir populations did not suffer from summer drought stress at Zbiroh for obvious reasons (Figure8).

Figure 6. Climate chart of the trial Zbiroh (mean annual data for 1961–1990: temperature 7.2^◦C;

precipitation: 586 mm). Note the quantity and seasonal distribution of precipitation with a summer maximum.

Figure 7.Climate chart of the weather station Everett, Washington (mean annual data for 1961–1990:

temperature 10.3^◦C; precipitation: 950 mm). Note the “Sub-Mediterranean type” distribution of rainfall with minimum precipitation in July.